1. Field of the Invention
This invention relates to magnetostrictive filters and, more particularly, to magnetostrictive rod filters in which the magnetostrictive rod is able to vibrate freely.
2. Description of the Prior Art
Filters with magnetostrictive rods have already been studied. An article by H. H. HALL was published in the Proceedings of the Institute of Radio Engineers, volume 21, No. 9, September 1933, pp. 1328-1338. Then two articles by A. P. THIELE describe such filters: "Narrow band magnetostrictive filters" in "Electronic and Radio Engineer", November 1958, pages 402-411 and "Magnetostrictive filters" in Electronics, June 1959, pages 72-74. These types of filters are basically formed of a magnetostrictive rod placed inside a glass or plastic sheath and surrounded by two separate windings. Each winding is placed on one or the other side of the center of the bar. Permanent magnets are judiciously placed to create a permanent field inside the rod.
However, these types of filters have attenuation curves which have no pole, i.e. no infinite attenuation point and thus cannot be often used in industry.
The purpose of this invention is to mitigate the defect and to construct magnetostrictive rod filters having attenuation poles and, in addition, to place the attenuation poles at the frequency positions required by the technology, in relation to the zeros of the attenuation curve.